The field of the invention is positioning systems. More particularly, the field of the invention is positioning systems utilizing a linear voltage displacement transducer and a DC planetary gear motor.
There are numerous machines where a member is cyclically driven and it is required to stop the member at a precise location within its positional cycle. One such type of machine is a terminating unit, which is utilized repetitively to attach terminals to the end of one or more wires, such as those used in power distribution and communications. These units typically incorporate a motor that is attached via a mechanical linkage to a movable member, such as a vertical ram. The mechanical linkage transforms the rotary motion of the motor to the linear motion of the ram, which provides the required force for crimping the terminal to the wire. During this process, it is often necessary to momentarily hold the ram in a desired position using a positioning system. For example, it may be desirable to hold the ram near the bottom of its cycle so that a wire may be placed within the connector for termination.
Methods of holding a desired position on a terminating unit typically rely on limit switches, rotary encoders or resolvers to monitor the rotational position of the motor. Systems of this type either turn the motor off at the desired position, using system friction to maintain the desired position or using a bi-directional motor system that reverses the drive of the motor to hold the ram in position. For example, a single cycle positioning system may be used that incorporates a three phase induction motor having a three phase inverter and a microprocessor for controlling the inverter to generate three phase power. Pulse width modulation techniques are utilized along with start, stop, and direction signals to control the forward or backward force applied to the ram.
The use of such systems to control positioning may be costly and can be unreliable. Also, indirect monitoring of the ram by monitoring the rotation of the motor may lead to positional inaccuracies imparted by the mechanical link between the motor and the ram. Accordingly, an improved system is needed.